Wastewater –Its Journey to Treatment and Return to the Environment

Where does it all go!

Where does the water from the washer go?

When you flush the toilet where does the contents go?

By gravity flow, the waste is on its way to your local wastewater treatment plant!

Why treat wastewater?

• Causes a demand for dissolved oxygen (lower DO levels of streams)

• Adds nutrients (nitrate and phosphate) to cause excessive growth

• Increases suspended solids or sediments in streams (turbidity increase)

Levels of Treatment

Primary– removal by physical separation of grit and

large objects (material to landfill for disposal)

Secondary– aerobic microbiological process (sludge)

organic matter + O2 CO2 + NH3 + H2O

NH3 NO3-

- lowers suspended solids content (into sludge)

aquatic nutrient

Mostly dead microbes

Aeration and

rapid mixing

Settlingcollects sludge

on bottom

Secondary process

airdiffuser

From

pri

mary

pro

cess

To te

rtiary

pro

cess

Levels of Treatment continuedTertiary (advanced)– anaerobic microbiological process with a

different microbe where O2 is toxic (more sludge)

NO3- N2 (escapes to atmosphere)

– PO4-3 if not removed in sludge in secondary

processPO4

-3 + Al+3 AlPO4 (s) (into sludge)

- aeration to strip N2 and re-oxygenate (add DO)

Slow mixingto keep

suspended and O2 out

Settlingcollects sludge

on bottom

Tertiary processFr

om

seco

ndary

pro

cess

Effl

uent

add methanol as food source

When the treatment is done…

• Effluent back to stream after– a final carbon filtration and– chlorination/dechlorination

• Sludge – very nutrient rich– applied directly to land as fertilizer– incinerated (good fuel after drying)– composted